Computational study of the effect of core–skin structure on the mechanical properties of carbon nanofibers

Abstract

The effect of the core-skin structure on the mechanical properties of carbon nanofibers is investigated in large-scale molecular dynamics simulations of tensile deformation of carbon nanofibers with the core-skin and homogeneous structures. Contrary to an established notion of the deleterious effect of the skin layer on the strength of carbon fibers, the presence of a high-quality skin layer is found to increase both the Young's modulus and tensile strength of the nanofiber. A detailed analysis of the fracture process indicates that the nanofiber strengthening is related to the ability of skin layer to suppress crack nucleation at the core-skin interface. The computational predictions suggest that the design of new approaches to carbon fiber manufacturing and processing leading to the generation of a high-quality skin layer while avoiding the introduction of structural defects at the core-skin interface may yield a significant enhancement of the mechanical properties of carbon fibers.

Atomistically informed hierarchical modeling for revisiting the constituent structures from heredity and nano–micro mechanics of sheath-core carbon fiber

“…Parameterized piecewise energy expression families are written in eqn (6), considering the piecewise continuity and asymptotic behaviors toward the zero bonding potential energy. The conjunction point r critical was solved equating the derivatives of the harmonic and logistic functions in eqn (7) and (8) to create force expressions. We introduced an additional variable z to regulate the shape of the modified logistic function and we noticed that the curve exhibited better stiffness features taking z = 4 than the Morse force field from the enlarged view in Fig.…”

“…No evident strain rate dependency on the mechanical properties is observed; thus, these properties take the average value among samples under various strain rates. Unlike the organic system whose instantaneous modulus depends on dynamic loading frequency and strain rate due to the α and β relaxations 57 with clear scaling trends, 58 the reported axial modulus of brittle materials such as graphene or carbon nanotube becomes less sensitive to strain rates 8 considering the complex competitive roles of hardening effects from restraining crack propagation and softening effects from local non-isothermal damage. 59 These effects become less conspicuous under ultrahigh strain rates and room temperature with slight thermal fluctuations.…”

“…Interfacial areas between misoriented flaws and ideal basal planes were identified as the fracture initiation areas during the tensile process, and the Reynolds-Sharp mechanism 7 of shear stress failure was captured within linear elastic fracture mechanics. He et al 8 generated concentric cylindrical carbon nanofiber models with multi-walled carbon nanotube skin layer, amorphous carbon core region imitating HRTEM fingerprint patterns, and microcracks at the skin-core interface. Joshi et al 9 drew on the idea of ''building blocks'' modeling and artificially arranged orientation angles, amorphous carbon region, and the grain boundaries to construct combinational parallel-series polycrystalline annealing model featured with grain boundaries and vacancies.…”